The present invention relates to a light tracking device for driving one or more light receiving elements to track a light source. Particularly the invention has application in the field of solar concentrators, where the tracking device can be used to drive one or more solar-light-to-energy converting devices to track the path of the sun.
Solar power is an extremely abundant source energy. Photovoltaics are used to convert the sunlight into electrical energy. Solar photovoltaic systems do not produce CO2 emissions in use and hence are a potentially interesting source of power in the future.
However, photovoltaics are expensive to produce and therefore as an investment, it can take more than 10 years for a photovoltaic installation to repay its capital costs, and hence such systems have not historically been an attractive source of power.
To address this issue, it has been considered to use solar concentrating systems. A solar concentrating system collects direct sunlight and focuses or concentrates it into a smaller area. Expensive photovoltaic (PV) material is only placed at the point where the light is concentrated, and hence the amount of photovoltaic material used in a system of given dimensions is greatly reduced. Types of photovoltaic cell that operate well under high concentration ratios are suitable for this application. These include efficient “multiple junction” cells made by companies such as Spectrolab Inc. in the USA, that operate under several hundred times concentration ratio, or several hundred “suns”.
To concentrate sunlight, the optical system needs to track the sun as it moves across the sky. Known mechanical systems for solar tracking are typically variations on two basic mechanisms that both provide 2 axes of rotation. Both are based on a gimbal type arrangement.
The first consists of a post (typically vertical) that can rotate about its own axis, and a device mounted onto the post that tilts about a horizontal axis. The combination of the tilt and rotation of the device allows it to track the seasonal and daily movement of the sun. A schematic diagram of this type of system is shown in FIG. 1 and an example of this type of device can be found in the U.S. Pat. No. 5,730,117.
The second type of device consists of two axes that could be both horizontal in the initial position. The components are mounted as shown in FIG. 2. An example of such a system is described in the U.S. Pat. No. 4,968,355. In U.S. Pat. No. 4,968,355 the general principle of the angular motion is configured in an array format to enable larger scale installations at lower cost.
However, mechanical tracking systems have typically added significant cost to the final devices. Also, there are concerns about maintenance and the long term reliability of jointed mechanical systems in dusty environments. Furthermore, due to the large angle range over which the sun moves, the motion of such systems typically means that they occupy a large volume. A system that is low profile, i.e. is thin in one dimension both in use and in transport, has advantages. For example low profile systems have lower transportation costs as completed units. They are suitable for roof-top mounting because when they are installed they do not increase the cross section presented to the wind, and hence do not increase the likely wind loads imposed on the structure of the building, and have good aesthetic qualities.